Muffler



Jan. 7, 1936. w. A, woon El AL MUFFLER Original Filed Nov. 30, 1928 Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE MUFFLER Application November 30, 1928, Serial No. 322,681 Renewed March 6, 1934 1 Claim.

This invention relates to muillers or silencing devices for damping disagreeable noises incident to the operation of an internal combustion engine.

In addition to the explosion noises which vary in frequency and loudness with different engine speeds, there exists in most exhaust systems a deep bass roar or bellow which is of a fixed or constant frequency at all engine speeds. This m roar has been attributed, by some, to the tendency of the whole column of gas to take up a steady vibration, but after careful investigation, it appears to us, although not conclusively, that this roar emanates from the engine cylinders. However, its origin is immaterial for whatever the cause, the noise is objectionable, particularly in these days when the aim of all motor car manufacturers is to build quiet and smooth running engines. A partial remedy may be obtained a by some method of reducing the frequency or rate of vibration to the point where only a beating or throbbing sensation is presented to the auditory nerves.

It was during the course of certain extensive 3 experiments dealing with muilling apparatus that we discovered that the roar could be entirely eliminated by the provision of a device for atfecting the union of two sets of sound waves having the same rate of vibration but in oppogo site phase. The composition of two vibrating columns of opposite phase, but of the same period and amplitude, gives a zero resultant or, in other words, causes destruction of both vibrations. When two sound waves meet in opposite phase as the condensations of one coincide with the rarefactions of the other and establishes an equilibrium, whereby the sound at the meeting places is extinguished by interference.

The accomplishment of this result is perhaps 40 best efiected by the use of a reflecting chamber of a size correspondingto one fourth the length of the sound waves to be damped. The direct and reflected sound waves will thus meet in, opposite phase and the composition oi. the two 45 smooths out the pulsations and quenches the sound. For multiple resonance two or more chambers can be used.

The invention will be better understood upon reference to the accompanying drawing, wherein 50 Figure l is a longitudinal sectional view of an improved muiiler construction embodying the present invention. Figure 2 is a sectional view of a modified muiller structure in which a central tubular element forms two reflecting chambers.

65 Figure 3 is a view partly in section showing the invention applied at a different point in the ex-- haust system. Figure 4 is a sectional view illustrating an alternative arrangement, and Figure 5 is a sectional view of an adjustable reflecting chamber.

In the drawing, the numeral l indicates a tubular or cylindrical casing provided at its front end with a funnel shaped member 2 for connection with the exhaustpipe leading from the internal combustion engine, and at its rear end with a m funnel shaped member 3 for connection with a tail pipe leading to free atmosphere. In the funne] 2 is secured a twister blade assembly 4 which gives to the incoming gases a spiral motion into the muflier, which motion is continued throughout the length of the muiiie by the passage of the gases along inclined deflecting surfaces adjacent the several openings formed in a series of spaced walls 5. The walls 5 are preferably formed from a flat ring or disc of sheet metal, with inclined vanes or blades 6 punched or pressed out of the plane thereof so as to provide openings through the walls and inclined guiding surfaces for swirling the gases. The swirling motion given to the gases increases the effective length of the path of travel through the muiiier, and the movement past the several bailie walls serves to thoroughly break up and muilie the explosion noises. Within the funnel member I at the rear of the muiiier is located a twister blade assembly I, whose blades extend in a direction opposite to that of the twister assembly 4 in order that the swirling gases on reaching the end of the muiiier may be straightened out and flow straight through the tail pipe. Extending axially within the muiile casing l and through the several baflle walls 5 is a pipe or tube 8, closed at its rear end by a plug or wall 8. The distance between the open end of the pipe and the wall 8 is equal to approximately one quarter the length of those sound waves of a fixed frequency, that are perceptible as the roar before discussed. A part of these constant frequency sound waves enter the tube 8 and strike the wall 9, and are then reflected back to the open end of the tube where they meet with the direct sound waves in opposite phase. The union of the direct and reflected sound waves at a point where the condensations of one coincide with the rarefactions of the other annihilates both, or in other words smooths out the pulsations and extinguishes the roar.

In some instances, certain engines may be found to have two separate and distinct sound waves each of constant period and amplitude of its own. and in the event two of such noises are present then two reflecting chambers should be provided. As an illustration of a satisfactory arrangement for two such chambers, Figure 2, shows a single tube Ill, having a dividing wall ll intermediate its ends, and which may be embodied in a muilier construction similar to that shown in Figure 1. It will be understood, of course, that the distance between the wall I I and the opposite ends of the tube It) will be dependent upon the length of the sound waves to be smoothed out.

, While for convenience, the sounding chamber in commercial production would probably be built in as apart of the muiiier' assembly, it may be located elsewhere in the exhaust system. As an illustration of this, Figure 3 shows the exhaust pipe l2, that leads into muiller l3, as having a pair of closed end tubes or pipes l4 and [5, each of a difierent length. One, two, or more of such closed end pipes may beassociated with the exhaust dependent upon whether there are single or multiple tones to be eliminated. Each of such closed end tubes would of course,-be of a length corresponding to one quarter the length of the particular wave length for which it is intended.

The invention, however, is not limited to .closed end tubes orreflecting chambers, as it will be evident thatthe same result can be achieved by other means for dividing the sound waves and subsequently reuniting them in an opposite phase. One way of accomplishing this would be to provide the straight exhaust pipe 16 (Figure 4) with a return passageway, or one leading from and then back again to the interior of the pipe at spaced apart points as would be afiorded by the arcuate pipe 91. The time interval or diiference between the time it takes the sound waves to pass through the pipes l1 and the pipe 16 between the two openings, if equal to one half the vibration period, would result in a smoothing out of the vibrations.

Figure 5 illustrates an adjustable reflecting chamber wherein a piston I8 is slidable in a pipe or passageway l9 opening into exhaust pipe 20. By moving the piston l8 in and out and observing the results, probably with the aid of a sound 5 amplifier, the wave of the objectionable roar may be accurately determined and piston fixed in a permanent position of adjustment for dampen ingsuch roar. The use of such an adjustable piston is no doubt limited to laboratory or ex- 10 perimental work, because after the length of the sound wave to be smoothed out is once indicated,

it 'will be known that the reflecting chamber must definitely be one quarter of this length, and

it is more convenient for commercial production to provide a chamber having a fixed length which can be readily applied to the exhaust system.

While the invention has been described in terms that are more or less specific, it will be understood that it is not limited to the specific details shown and described, but that various modifications may be made such as'come within the scope'oi the appended claim.

We claim: a

A muflier for silencing explosion noises for use with an internal combustion engine, including, a casing for the flow of exhaust gases, a series of baflie walls within the casing for breaking up sound waves of varyingfrequencies, a tube extending axially of the casing and being supported by said walls, a partition wall at an intermediate point withinsaid tube providing on opposite sides thereof a pair of tuning chambers, each tuning chamber being ofa pre-determined length equal to one quarter that of a certain sound wave of a constant frequency at all engine speeds, whereby to damp the wave train by out of phase reflection.

WALTER A. woon. JOHN 0.1mm. 4o 

